Scientists at Mass General Hospital in Boston recently published findings on 1,150 adult patients in their hospital who underwent thymectomy (removal of the thymus gland). 

The thymus gland is a bit of a mysterious organ found in our chest that is most active in early childhood.  It is located in the chest between the lungs and just above the heart.  In infants the gland is large and completely covers the front of the heart. 

Until this recent study scientists have thought that the thymus played its key role in immune development in childhood and then withered away.  After puberty the gland shrinks to a very small size and is replaced by fat.  To surgeons it looks like a little blob of fat. 

In the Harvard study 2,300 adults had chest surgery and in 1,150 of them the thymus was removed during the surgery because “it was in the way” and was not felt to be needed.

For years, the thymus was felt to be only active during childhood.  It pumps out T lymphocytes, immune cells that have many functions.  The “new” T-cells can be formatted to do a variety of immunologic jobs.  Adults rely on memory T-cells, which are long lived cells that can be re-directed (teach an old dog new tricks) for special tasks.  Because of this “standard model of thymic function “the surgeons did not think removing it would be of consequence.  But it turns out that they were wrong. The thymus is not expendable after all. 

Within five years after surgery 8 percent of the thymectomy patients died compared to 3 percent of those whose thymus was not removed during the operation.  Cancer risk within 5 years was also double in the thymectomy group.  Finally, the thymectomy group had double the incidence of new auto-immune diseases. 

Needless to say, the Harvard scientists were shocked by these findings.  It is unclear what removal of the thymus changed.  Perhaps the “blob of fat” is still producing a few new T-cells.  Or perhaps the involuted thymus still subserves some type of immune-protective-surveillance not yet recognized.  At any rate these findings have led to both a change in surgical tactics and also new immunologic research to study thymic function in adults.